Those who are exposed to large quantities of airborne allergens can develop a serious inflammation of the lungs known as alveolitis. In this disorder it is not the tubes leading to the lung that are affected (as in asthma) but the lungs themselves. Tiny air-sacs known as alveoli perform the actual work of the lung in extracting oxygen from the air and passing it to the blood. If an allergic reaction to airborne allergens occurs in the alveoli, the large number of immune complexes produced can be deposited there and cause highly damaging inflammation. The structure of the alveoli begins to break down, causing shortness of breath,-tightness in the chest, fever and a dry cough.